Thread: cast vs aluminum heads

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If I switch my 383 from cast heads to aluminum ,How much can I safely raise
the compression ? What are the general rules when making this switch?
Thanx Ed

Generally speaking, you can run 1 pt more compression with aluminum heads. But it all comes down to your DCR. Stay under 8.5 and you should be fine with premium gas. I run 10.6 Static compression with 8.46 Dynamic compression. No problems with 92/93 octane.

Originally Posted by rumrumm

Generally speaking, you can run 1 pt more compression with aluminum heads. But it all comes down to your DCR. Stay under 8.5 and you should be fine with premium gas. I run 10.6 Static compression with 8.46 Dynamic compression. No problems with 92/93 octane.

Thank you for posting this information. I've been trying to get the relationship between SCR, DCR, squish, cranking compression and octane from other folks. I know how it works on my stuff, I just wanted to get a feel for the combinations others use. Do you know your cranking compression with this combination? Have you tried to run the motor on less octane?

I think I've been "leaving some on the table" with my conservative ideas.

Maybe?..... but like the old bull and the young bull on the hill...I like the old bulls idea better, later on when guys have more exsperiance they can decide whether to walk or run down the hill depending on their needs. ....I do get 1 warning before I get banned right ?

I have not tried to run 89 octane because I am "on the edge" so to speak of being able to successfully run 92/93 octane. But I built the engine knowing that would be the case. It has a .039 quench area, AFR 190 heads, a CompCams 280 Magnum cam, Edelbrocks RPM intake and 750 carb. I a very satisfied with the performance and its street manners.

I also have question on compression. I did a leak down test on my engine and all was good but i was wondering at 180 psi how do i figure out my compression?

You cannot determine compression that way. You have to know things like your head volume in cc's, type of piston, head gasket thickness, and deck height--normally you can assume a stock deck height is about .025. Try going here and using their calculator: http://www.newcovenant.com/speedcraf...ssionratio.htm

Originally Posted by rumrumm

I have not tried to run 89 octane because I am "on the edge" so to speak of being able to successfully run 92/93 octane. But I built the engine knowing that would be the case. It has a .039 quench area, AFR 190 heads, a CompCams 280 Magnum cam, Edelbrocks RPM intake and 750 carb. I a very satisfied with the performance and its street manners.

I.M.O.,a cam with similar duration and lift but with a 106 lobe seperation and would solve your problem.

Thanks for the post, Erik. You're right about the lobe center, but since I run power brakes, I was concerned about vacuum.

Originally Posted by rumrumm

Thanks for the post, Erik. You're right about the lobe center, but since I run power brakes, I was concerned about vacuum.

Do you have room for an aux. canister?

No, I don't. There is so little room anywhere inside or under a '32 Ford body that I didn't want to deal with one.